Primary ignition current (using a low-amp current clamp)

How to perform the test

Connect the low-amp current clamp to Channel A of the PicoScope. Select the 20 A range if available and switch the current clamp on. remeber to zero the clamp before connecting it to the circuit.

The current clamp should be placed directly onto the coil's supply cable and not around the loom that will also contain the negative (or negatives depending on the ignition system). The connection is illustrated in Figure 1.

With the example waveform displayed on the screen you can now hit the space bar to start looking at live readings.

Example waveform

Waveform notes

The waveform will show a curving line that indicates the speed at which the coil is being saturated. The flatter the line, the longer it is taking to magnetize the coil. The waveform flattens out for a time, where the current is being maintained by the amplifier once it has reached its requisite current. The current is held until the amplifier releases the earth path and the waveform then drops vertically. This vertical line is equally important, as a sloping line indicates that the amplifier is not switching fast enough and the induced voltage will suffer as a result.

The example waveform shows the current limiting circuit in operation. The current switches on as the dwell period starts and rises until the requisite 8 amps is achieved within the primary circuit, at which point the current is maintained until it is released at the point of ignition.

The dwell will expand as the engine revs are increased. This is to maintain a constant coil saturation time, hence the term 'constant energy'. If the vertical rulers are used and one is placed at the beginning of the dwell period and another placed on the induced voltage line, the coil saturation time can be measured. This will remain exactly the same regardless of engine speed.

Technical information

The purpose of the ignition amplifier is to switch the relatively high primary current of approximately 8 to 10 amps to earth when the component receives a signal from either the pick-up or Electronic Control Module (ECM).The output from the coil is determined by the speed of the switching. The faster this occurs, the greater the induced voltage into the coil's primary winding. The amplifier can best be described as a solid-state relay, allowing a small current to switch a much higher current. Due to this high amperage, the component will get hot, and a liberal application of heat transfer grease should be applied to the mating surface to dissipate the heat. Without this precaution the component will overheat and fail. The earth connection is crucial to the correct operation of the amplifier. An earth path waveform and topic can be found in the main menu.

The amplifier can also be referred to as a 'module' or an 'igniter' (Japanese term).

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered
to be correct. This information is an example of our investigations and findings and is not a definitive procedure.
Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test
settings.